Optical disc drive

ABSTRACT

An optical disc drive according to the present invention reads and/or writes data from/on an optical disc having at least one information layer with a light beam and includes: a spherical aberration detecting section for generating a spherical aberration signal representing a spherical aberration produced at a focal point of the light beam on the information layer of the disc; a spherical aberration changing section for changing the spherical aberration; a spherical aberration regulating section for generating an aberration correction signal to correct the spherical aberration by driving the changing section; and means for detecting a value of the aberration correction signal that minimizes the spherical aberration when the focal point of the light beam is located on the information layer of the disc and for detecting the depth of the information layer, which corresponds to a distance from the information layer on which the focal point of the light beam is located to the surface of the disc, based on the value.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Section 371 of International Application No.PCT/JP03/00447, filed Jan. 20, 2003, the disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an optical disc drive for readingand/or writing data from/on a disklike information storage medium (whichwill be referred to herein as an “optical disc”) rotating. Moreparticularly, the present invention relates to an optical disc drivethat can recognize multiple types of optical discs when started up.

BACKGROUND ART

Data can be read out from a rotating optical disc by irradiating theoptical disc with relatively weak light beam having a constant quantityand detecting the light that has been modulated by, and reflected from,the optical disc. On the other hand, in writing data on a recordable orrewritable optical disc, data is written there by irradiating theoptical disc with a light beam, of which the quantity has been changedaccording to the data to be written, and locally changing the propertyof a storage material film. Such optical disc read and write operationsare described in Japanese Laid-Open Publication No. 52-80802, forexample.

On a read-only optical disc, information is already stored as pits thatare arranged spirally during the manufacturing process of the opticaldisc. On the other hand, on a readable and rewritable optical disc, astorage material film, from/on which data can be read and writtenoptically, is deposited by an evaporation process, for example, on thesurface of a substrate on which tracks, including spiral concave orconvex portions, are arranged.

It should be noted that the depth or height of the pits, the depth ofthe concave portions of the tracks or the height of the convex portionsof the tracks, and the thickness of the storage material film are allfar smaller than the thickness of the optical disc substrate. For thatreason, those portions of the optical disc, where data is stored, definea substantially two-dimensional plane, which will be referred to hereinas a “storage layer”. Any optical disc includes at least one suchstorage layer.

To read or write data from/on a readable and rewritable optical disc,the light beam always needs to maintain a predetermined converging stateon a storage layer. For that purpose, a “focus control” and a “trackingcontrol” are required. The “focus control” means controlling the focalpoint of a light beam perpendicularly to the surface of a given opticaldisc (which direction will be referred to herein as a “focusingdirection”). On the other hand, the “tracking control” means controllingthe focal point of a light beam along the radius of a given optical disc(which direction will be referred to herein as a “tracking direction”)such that the light beam spot is always located right on a target track.

Next, a conventional optical disc drive will be described with referenceto FIG. 1. The optical disc drive shown in FIG. 1 is an apparatus thatcan read and/or write data from/on a loaded optical disc 1 and includesa mechanism for rotating the optical disc 1 with a motor (not shown), anoptical head 10 for irradiating the rotating optical disc 1 with light,and a signal processing and control section, which exchanges electricalsignals with the optical head 10.

The optical head 10 includes a laser light source 11, a condenser lens13, a polarization beam splitter 12, a focus actuator (which will bereferred to herein as an “Fc actuator”) 14, a tracking actuator (whichwill be referred to herein as an “Tk actuator”) 15, and a photodetector16.

A light beam, which has been emitted from the laser light source 11, istransmitted through the polarization beam splitter 12 and then focusedonto the disklike optical disc 1 by the condenser lens 13. After havingbeen reflected from the optical disc 1, the light beam is passed throughthe condenser lens 13 again, reflected from the polarization beamsplitter 12 and then incident onto the photodetector 16.

When current is allowed to flow through the Fc actuator 14, thecondenser lens 13, supported by an elastic body (not shown), moves inthe focusing direction due to an electromagnetic force. On the otherhand, when current is allowed to flow through the Tk actuator 15, thecondenser lens 13 moves in the tracking direction.

The photodetector 16 outputs a light quantity signal to a focus errorgenerator (which will be referred to herein as an “FE generator”) 30, atracking error generator (which will be referred to herein as a “TEgenerator”) 40, a reflected light quantity detector 66, a wobbledetector 83, and a disc type information reader 84.

The FE generator 30 functions as a focus error signal detecting sectionand generates an error signal representing the focusing state of thelight beam with respect to the information layer of the optical disc 1based on the light quantity signal supplied from the photodetector 16.The error signal is obtained, through computations, as a signalrepresenting the deviation of the focal point of the light beam from theinformation layer of the optical disc 1 (which will be referred toherein as an “FE signal”). The FE signal is transferred to the Fcactuator 14 by way of a focus control filter (which will be referred toherein as an “Fc filter”) 31 and a focus control driver (which will bereferred to herein as an “Fc driver”) 32, which function as a focuscontrol driving section. The Fc filter 31 and Fc driver 32 perform phasecompensation to get the focus control done with good stability.

In accordance with the FE signal supplied from the Fc driver 32, the Fcactuator 14 drives the condenser lens 13 in the focus direction suchthat the light beam is focused in a predetermined state on a certaininformation layer of the optical disc 1, which is so-called “focuscontrol”.

The TE generator 40 functions as a tracking error detecting section andgenerates an error signal representing a positional relationship betweenthe light beam spot on the optical disc 1 and the track (which will bereferred to herein as a “TE signal”) based on the light quantity signalsupplied from the photodetector 16. The TE signal is transferred to theTk actuator 15 by way of a tracking control filter (which will bereferred to herein as an “Tk filter”) 41 and a tracking control driver(which will be referred to herein as an “Tk driver”) 42. In accordancewith the TE signal supplied from the Tk driver 42, the Tk actuator 15drives the condenser lens 13 in the tracking direction such that thelight beam spot follows the tracks, which is so-called “trackingcontrol”.

In accordance with the signal supplied from the photodetector 16, thereflected light quantity detector 66 detects the quantity of the lightthat has been reflected from the optical disc 1 and outputs thereflected light quantity value detected to a disc type recognizer 85. Inresponse to the signal supplied from the photodetector 16, the wobbledetector 83 detects the amplitude of micro wobbling (which will bereferred to herein as “wobble”) of the tracks on the optical disc 1 andoutputs the amplitude value detected to the disc type recognizer 85. Onreceiving the signal from the photodetector 16, the disc typeinformation reader 84 reads the optical disc information, which waswritten in advance on the optical disc 1, and transmits the optical discinformation to the disc type recognizer 85.

Based on the signals supplied from the reflected light quantity detector66, wobble detector 83 and disc type information reader 84, the disctype recognizer 85 recognizes the type of the given optical disc 1.

Suppose the reflectance of the optical disc changes with the type of thedisc. In that case, even if the given optical disc 1 is irradiated witha light beam having the same intensity, the quantity of light reflectedchanges according to the reflectance of that optical disc 1.Accordingly, by comparing the quantity of the light reflected from theoptical disc 1 with a predetermined level, the type of the given opticaldisc 1 can be recognized by the specific level of the reflectance of theoptical disc.

Also, some types of optical discs may have the wobble but others not.Accordingly, if it is determined, by detecting the wobble amplitude ofthe given optical disc 1, whether or not the wobble is present on thatoptical disc 1, the type of the given optical disc 1 can be recognized.

Furthermore, information about a disc type may be stored on some opticaldiscs. Thus, the type of the given optical disc 1 may be recognized byreading the optical disc information.

Hereinafter, another conventional optical disc drive will be describedwith reference to FIG. 2. In FIG. 2, any component, having the samefunction as the counterpart shown in FIG. 1, is identified by the samereference numeral as that used in FIG. 1 and the description thereofwill be omitted herein.

The apparatus shown in FIG. 2 includes a disc type recognizer 67functioning as disc type recognizing means. The disc type recognizer 67recognizes the type of a given optical disc in accordance with a signalsupplied from a reflected light quantity detector 66 and outputs asignal, representing the result of recognition, to a best opticalwavelength selector 87.

The disc type recognizer 67 sends a low-level signal to an opticalwavelength selector 90 while still recognizing the type of the opticaldisc, but sends a high-level signal to the optical wavelength selector90 after having recognized the type of the optical disc.

A best optical wavelength table 86 stores information about the bestoptical wavelengths for multiple types of optical discs, from/on whichthis optical disc drive can read and/or write data. Also, the bestoptical wavelength table 86 provides the optical wavelength informationfor a best optical wavelength selector 87 and an initial opticalwavelength selector 88.

The best optical wavelength selector 87 selects one of the best opticalwavelengths in accordance with the recognition result of the disc typerecognizer 67 and the optical wavelength information stored in the bestoptical wavelength table 86, and then outputs a signal, representing theoptical wavelength selected, to the optical wavelength selector 90.

A selection index generator 89 supplies an index signal to the initialoptical wavelength selector 88 so as to instruct the initial opticalwavelength selector 88 to select the longest wavelength. In response tothe index signal supplied from the selection index generator 89, theinitial optical wavelength selector 88 selects the longest opticalwavelength in accordance with the optical wavelength information storedin the best optical wavelength table 86 and supplies a signal,representing the wavelength selected, to the optical wavelength selector90.

If the signal supplied from the disc type recognizer 67 is low, theoptical wavelength selector 90 selects the optical wavelength, providedby the initial optical wavelength selector 88, for the laser lightsource 11. On the other hand, if the signal supplied from the disc typerecognizer 67 is high, the optical wavelength selector 90 selects theoptical wavelength, provided by the best optical wavelength selector 87,for the laser light source 11. In response, the laser light source 11,including multiple types of semiconductor laser diodes, for example,radiates a light beam having the specified optical wavelength.

Suppose an optical disc, from/on which data should be read or written ata long optical wavelength, has been loaded into an optical disc drive.In that case, if the optical disc is irradiated with a light beam havinga short optical wavelength during a startup process, then the data maybe lost from the optical disc, which is a problem. The lost data has alength corresponding to approximately one-fourth to one-half rotation ofthe optical disc. Accordingly, even if error correction were made, thelost data could not be correctible and could not be read at all. Amongother things, a storage material film, which is optimized to a longoptical wavelength, causes such a problem particularly easily becausesuch a film absorbs a lot of light with short wavelengths. To overcomesuch a problem, a technique of using a long wavelength before the typeof the given optical disc is recognized was proposed. A conventionaloptical disc drive of that type is disclosed in Japanese Laid-OpenPublication No. 11-176073, for example.

Hereinafter, still another optical disc drive will be described withreference to FIG. 3. In FIG. 3, any component, having the same functionas the counterpart shown in FIG. 1, is identified by the same referencenumeral as that used in FIG. 1 and the description thereof will beomitted herein.

The apparatus shown in FIG. 3 includes a focusing instructor 77 and acontrol switch 78, which together functions as focusing means, and asearch drive generator 79 functioning as search driving means.

The output of an FE generator 30 is supplied to an Fc filter 31 and thefocusing instructor 77. The output signal of the Fc filter 31 issupplied to the control switch 83. In the initial state, the focusinginstructor 77 sends a low-level signal to the control switch 78.However, after the FE signal supplied from the FE generator 30 hasexceeded a predetermined level and decreased to less than a zero-crosspoint, the focusing instructor 77 sends a high-level signal to thecontrol switch 78. The search drive generator 79 supplies a drivesignal, which will move the condenser lens 13 toward the optical disc 1,to the control switch 78.

If the signal supplied from the focusing instructor 77 is low, then thecontrol switch 78 passes the output signal of the search drive generator79 to the Fc driver 32. On the other hand, if the signal supplied fromthe focusing instructor 77 is high, then the control switch 78 passesthe output signal of the Fc filter 31 to the Fc driver 32.

Next, it will be described with reference to FIG. 4 how the optical discdrive shown in FIG. 3 performs a focusing operation. Portion (a) of FIG.4 shows the output FE signal of the FE generator 30, portion (b) of FIG.4 shows the output signal of the focusing instructor 77, and portion (c)of FIG. 4 shows the sources of drive signals to be selected by thecontrol switch 78. In portions (a) through (a) of FIG. 4, the abscissarepresents the time.

Once a startup operation is started with an optical disc loaded into theoptical disc drive, the control switch 78 selects the drive signalsupplied from the search drive generator 79 in the initial state. Then,the focal point of the light beam that has been converged by thecondenser lens 13 is shifted toward the information layer of the opticaldisc 1. When the FE signal supplied from the FE generator 30 crosseszero after having exceeded a predetermined level FELVL, the outputsignal of the focusing instructor 77 changes from the low level into thehigh level. As of that moment, the control switch 78 selects the drivesignal supplied from the Fc filter 31, thus turning the focus controlON.

In a multilayer storage optical disc with a plurality of informationlayers on which information can be stored, the light beam needs to bedistributed uniformly to the respective information layers. For thatreason, the greater the number of information layers, the higher thetransmittance, but the lower the reflectance and absorbance, of eachinformation layer should be.

Also, in a rewritable optical disc, written and unwritten areas of eachinformation layer have mutually different reflectances. Accordingly, thequantity of reflected light detected changes depending on whether thespot of the light beam that has been radiated to recognize the type ofthe optical disc is located in an unwritten area or in a written area.Thus, the quantity of light reflected changes not only with the numberof information layers the given optical disc has but also with thespecific beam spot location on each information layer. For that reason,it is difficult to distinguish, just by the quantity of reflected light,several types of multilayer storage optical discs with different numbersof information layers from each other.

Furthermore, no matter how many information layers a multilayer storageoptical disc has, each and every information layer thereof has trackwobbles. Thus, it is difficult to distinguish, just by the wobbleamplitude, several types of multilayer storage optical discs withdifferent numbers of information layers from each other.

As described above, in a multilayer storage optical disc, as the numberof information layers increases, the transmittance of each storage layerneeds to be increased, and therefore, the reflectance and absorbance ofeach information layer both decrease. To compensate for such a decrease,as the number of information layers increases, the intensity of thelight beam radiated from a laser light source needs to be increased. Forthat reason, if the type of the given optical disc 1 is recognized byreading optical disc information from the optical disc, then theintensity of the light beam radiated from the laser light source needsto be changed after the type recognition. However, if the intensity ofthe light beam is changed, then it takes a longer startup time because alearning operation for reading the optical disc information must becarried out again.

Furthermore, in a multilayer storage optical disc, the best lightintensity of the light beam radiated from the laser light source changeswith the number of information layers as described above. If arewritable optical disc is exposed to a light beam with an excessivelyhigh intensity, then the information stored there may be altered. Also,if an optical disc is irradiated with a light beam, of which theintensity is higher than the best light intensity, before the type ofthe optical disc is recognized, then the information stored there willbe lost to a non-correctible degree.

Meanwhile, to further increase the storage density of optical discs, thedistance from the surface of an optical disc to an information layerthereof (which will be referred to herein as an “information layerdepth”) tends to decrease. In a multilayer storage optical disc that hashad its density increased in this manner, it is difficult to narrow thegap between the information layers so as to prevent the informationlayers from affecting each other. Thus, the variation in depth betweenthe information layers increases. If the information layer depth changesat a greater percentage, then the spherical aberration produced on eachinformation layer also changes more significantly. Hereinafter, thisproblem will be described with reference to FIG. 5.

FIG. 5 shows cross sections of two types of optical discs with mutuallydifferent information layer depths. Specifically, the optical disc shownon the left-hand side of FIG. 5 has a relatively deep information layer,while the optical disc shown on the right-hand side of FIG. 5 has arelatively shallow information layer. On each of these optical discs, afocus control is carried out such that the focal point of the light beamis located right on its information layer.

Suppose the light beam that has been converged by the condenser lens 13produces the smallest spherical aberration with respect to the opticaldisc shown on the left-hand side of FIG. 5. In that case, the light beamis focused at a point on the information layer in the optical disc shownon the left-hand side of FIG. 5. However, if the information layer depthis different as in the optical disc shown on the right-hand side of FIG.5, then the light beam is not focused at a point but a gap is createdbetween the focal point of the light beam passing the inside portion ofthe condenser lens 13 and that of the light beam passing the outsideportion of condenser lens 13, which is so-called “spherical aberration”.When such a spherical aberration is produced, the data that has beenread from, or written on, the information layer has deterioratedquality. Thus, the spherical aberration needs to be adjusted withrespect to the information layer on which the focal point of the lightbeam should be located.

In an apparatus of recognizing the type of a given optical disc based onthe optical disc information that has been stored on the optical disc,the time it takes to finish the type recognition increases by the timeto adjust the spherical aberration, thus extending the startup time ofthe optical disc drive unintentionally.

As described above, the magnitude of spherical aberration changes withthe depth of the information layer. In addition, if the sphericalaberration increases, the FE signal deteriorates and focusing becomesharder to accomplish.

In order to overcome the problems described above, an object of thepresent invention is to provide an optical disc drive, which can quicklyperform a start-up process on a rewritable multilayer optical disc.

DISCLOSURE OF INVENTION

An optical disc drive according to the present invention reads and/orwrites data from/on an optical disc, having at least one informationlayer, by using a light beam. The optical disc drive includes: aspherical aberration detecting section for generating a sphericalaberration signal representing a spherical aberration that has beenproduced at a focal point of the light beam on the information layer ofthe optical disc; a spherical aberration changing section for changingthe spherical aberration; a spherical aberration regulating section forgenerating an aberration correction signal to correct the sphericalaberration by driving the spherical aberration changing section; andmeans for detecting a value of the aberration correction signal thatminimizes the spherical aberration in a situation where the focal pointof the light beam is located on the information layer of the opticaldisc and for detecting the depth of the information layer, whichcorresponds to a distance from the information layer on which the focalpoint of the light beam is located to the surface of the optical disc,based on the value.

In one preferred embodiment, the optical disc drive further includescomparing means for comparing the value of the aberration correctionsignal, which minimizes the spherical aberration in the situation wherethe focal point of the light beam is located on the information layer ofthe optical disc, with a predetermined value.

In another preferred embodiment, if the optical disc, irradiated withthe light beam, has a plurality of information layers, the optical discdrive determines, based on a comparison result obtained by the comparingmeans, on which of the information layers the focal point of the lightbeam is currently located.

In another preferred embodiment, the optical disc drive recognizes,based on a comparison result obtained by the comparing means, the typeof the optical disc being irradiated with the light beam.

In another preferred embodiment, the optical disc drive detects, basedon a comparison result obtained by the comparing means, the number ofthe information layers that the optical disc being irradiated with thelight beam has.

In another preferred embodiment, the optical disc drive detects aquantity, corresponding to a distance from the surface of the opticaldisc to one of the information layers that is closest to the surface ofthe optical disc, thereby recognizing the optical disc being irradiatedwith the light beam based on the quantity detected.

In another preferred embodiment, if the optical disc, irradiated withthe light beam, has a plurality of information layers, the optical discdrive determines, based on a comparison result obtained by the comparingmeans and address information acquired from the information layer onwhich the focal point of the light beam is located, on which of theinformation layers the focal point of the light beam is currentlylocated.

In another preferred embodiment, the optical disc drive furtherincludes: converged beam irradiating means for converging the light beamand irradiating the optical disc with the converged light beam; a focusregulating section for shifting the focal point of the light beam, whichhas been converged by the converged beam irradiating means,perpendicularly to the information layers of the optical disc; a focuserror signal detecting section for generating a signal representing thedeviation of the focal point of the light beam from each saidinformation layer of the optical disc; and a focus control drivingsection for driving the focus regulating section in response to a signalsupplied from the focus error signal detecting section such that thefocal point of the light beam catches up with the information layer ofthe optical disc.

In another preferred embodiment, the optical disc drive furtherincludes: a tracking error detecting section for detecting a signalrepresenting a positional relationship between the focal point of thelight beam and a track on the optical disc; and an amplitude detectingsection for detecting the amplitude of a signal supplied from thetracking error detecting section. The spherical aberration regulatingsection drives the spherical aberration changing section so as tomaximize a signal supplied from the amplitude detecting section.

In another preferred embodiment, the spherical aberration regulatingsection drives the spherical aberration changing section so as to makethe signal supplied from the spherical aberration detecting sectionequal to zero.

In another preferred embodiment, the optical disc drive further includesa judging section for judging the validity of the spherical aberrationsignal supplied from the spherical aberration detecting section. Thespherical aberration regulating section drives the spherical aberrationchanging section such that the judging section recognizes the validityof the spherical aberration signal and then drives the sphericalaberration changing section such that the spherical aberration signalsupplied from the spherical aberration detecting section becomes zero.

In another preferred embodiment, the optical disc drive further includesjudging means for judging the validity of the spherical aberrationsignal supplied from the spherical aberration detecting section. Thespherical aberration regulating section drives the spherical aberrationchanging section such that the judging means recognizes the validity ofthe spherical aberration signal.

Still another optical disc drive according to the present inventionincludes: a converged beam irradiating section for converging a lightbeam and irradiating multiple types of optical discs, which use a lightbeam of the same wavelength to read information but have mutuallydifferent best light beam intensities, with the converged light beam; adisc type recognizing section for recognizing the type of a givenoptical disc; a best intensity storage section for storing the bestlight beam intensities of all type of optical discs to handle; and alight intensity setting section for setting a light beam intensity,which would not cause any alteration in the information stored on theinformation layer of any of the multiple types of optical discs tohandle, for the converged beam irradiating section if the disc typerecognizing section has not recognized the type of the given opticaldisc yet and also selecting one of the light beam intensities from thebest intensity storage section according to a recognition resultobtained by the disc type recognizing section that has alreadyrecognized the type of the given optical disc and setting the selectedlight beam intensity for the converged beam irradiating section.

In one preferred embodiment, the optical disc drive further includes anallowable intensity storage section for storing allowable light beamintensities, at or under which no alteration should occur in theinformation stored on any of the multiple types of optical discs tohandle. If the disc type recognizing section has not recognized the typeof the given optical disc yet, the light intensity setting sectionselects the weakest one of the light beam intensities from the allowableintensity storage section and setting the selected light beam intensityfor the converged beam irradiating section.

In another preferred embodiment, if the disc type recognizing sectionhas not recognized the type of the given optical disc yet, the lightintensity setting section selects the weakest one of the light beamintensities from the best intensity storage section and setting theselected light beam intensity for the converged beam irradiatingsection.

In another preferred embodiment, if the disc type recognizing sectionhas not recognized the type of the given optical disc yet, the lightintensity setting section selects one of the best light beamintensities, which is associated with a type of optical disc with thesmallest number of information layers, from the best intensity storagesection and setting the selected light beam intensity for the convergedbeam irradiating section.

Yet another optical disc drive according to the present inventionincludes: a converged beam irradiating section for converging a lightbeam and irradiating multiple types of optical discs, all of which havean area, having a micro wobbled track representing information andstoring no user information, at the same radial location, with theconverged light beam; a transport section for shifting the focal pointof the light beam, which has been converged by the converged beamirradiating section, along the radius of the optical disc; a disc typerecognizing section for recognizing the type of the given optical disc;and a transport driving section for generating a drive signal for thetransport section such that the area of the optical disc, from which theinformation stored as the micro track wobble is read, is irradiated withthe light beam if the disc type recognizing section has not recognizedthe type of the given optical disc yet.

In one preferred embodiment, the optical disc drive further includes: arotating section for rotating the optical disc; a focus shifting sectionfor shifting the focal point of the light beam, which has been convergedby the converged beam irradiating section, perpendicularly to theinformation layer of the optical disc; and a passage sensing section forsensing the focal point of the light beam passing through theinformation layer of the optical disc. While the rotating section hasnot started to rotate the optical disc yet, the disc type recognizingsection supplies a monotonically increasing or decreasing drive signalto the focus shifting section and counts the number of informationlayers in response to a signal supplied from the passage sensingsection.

Yet another optical disc drive according to the present inventionincludes: a converged beam irradiating section for converging a lightbeam and irradiating multiple types of optical discs, havingrespectively different numbers of information layers, with the convergedlight beam; a disc type recognizing section for recognizing a givenoptical disc as having an information layer at a particular depth; afocus shifting section for shifting the focal point of the light beam,which has been converged by the converged beam irradiating section,perpendicularly to the information layers of the optical disc; a focuserror signal detecting section for generating a signal representing thedeviation of the focal point of the light beam from each informationlayer of the optical disc; a focus control driving section forgenerating a drive signal for the focus shifting section such that thefocal point of the light beam catches up with a target information layerof the optical disc in accordance with a signal supplied from the focuserror signal detecting section; and an information layer selectingsection for, if the disc type recognizing section has recognized thegiven optical disc as a type having an information layer at a particularsubstrate thickness position, selecting the information layer at thesubstrate thickness position as the information layer, toward which thefocus control driving section controls the focal point of the lightbeam.

In another preferred embodiment, the disc type recognizing sectionrecognizes the given optical disc as an optical disc in which one of atleast one information layer, which is most distant from its surface, hasa uniform substrate thickness. The information layer selecting sectionincludes: a search driving section for generating a drive signal toinstruct the focus shifting section to bring the focal point of thelight beam away from a position close to the optical disc when the disctype recognizing section recognizes the given optical disc as an opticaldisc in which the information layer, most distant from its surface, hasthe uniform substrate thickness; and a focusing section for selectivelysupplying a signal either from the focus control driving section or thesearch driving section to the focus shifting section in response to thesignal supplied from the focus error signal detecting section.

In another preferred embodiment, the disc type recognizing sectionrecognizes the given optical disc as an optical disc in which one of atleast one information layer, which is closest to its surface, has auniform substrate thickness. The information layer selecting sectionincludes: a search driving section for generating a drive signal toinstruct the focus shifting section to bring the focal point of thelight beam from a distant position toward the optical disc when the disctype recognizing section recognizes the given optical disc as an opticaldisc in which the information layer, closest to its surface, has theuniform substrate thickness; and a focusing section for selectivelysupplying a signal either from the focus control driving section or thesearch driving section to the focus shifting section in response to thesignal supplied from the focus error signal detecting section.

Yet another optical disc drive according to the present inventionincludes: a converged beam irradiating section for converging a lightbeam and irradiating multiple types of optical discs, havingrespectively different numbers of information layers, with the convergedlight beam; a disc type recognizing section for recognizing the type ofa given optical disc; a spherical aberration changing section forchanging a spherical aberration to be produced at the focal point of thelight beam that has been converged by the converged beam irradiatingsection; a substrate thickness storage section for storing the substratethicknesses of all information layers of the optical discs; and aspherical aberration correction generating section for obtaining thesubstrate thicknesses of information layers, which could be present inthe optical disc, from the substrate thickness storage section based ona recognition result obtained by the disc type recognizing section andsupplying a drive signal, representing their average, to the sphericalaberration changing section.

Yet another optical disc drive according to the present inventionincludes: a converged beam irradiating section for converging a lightbeam and irradiating multiple types of optical discs, havingrespectively different numbers of information layers, with the convergedlight beam; a disc type recognizing section for recognizing the type ofa given optical disc; a spherical aberration changing section forchanging a spherical aberration to be produced at the focal point of thelight beam that has been converged by the converged beam irradiatingsection; a substrate thickness storage section for storing the substratethicknesses of all information layers of the optical discs; and aspherical aberration correction generating section for obtaining themaximum and minimum substrate thicknesses of information layers, whichcould be present in the optical disc, from the substrate thicknessstorage section based on a recognition result obtained by the disc typerecognizing section and supplying a drive signal, representing theiraverage, to the spherical aberration changing section.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a configuration for a conventionaloptical disc drive.

FIG. 2 is a block diagram showing a configuration for anotherconventional optical disc drive.

FIG. 3 is a block diagram showing a configuration for still anotherconventional optical disc drive.

Portion (a) of FIG. 4 shows an output signal of an FE generator in theconventional optical disc drive, portion (b) of FIG. 4 shows an outputsignal of a focusing instructor in the conventional optical disc drive,and portion (c) of FIG. 4 shows the sources of drive signals to beselected by a control switch.

FIG. 5 is cross-sectional views showing how a spherical aberration isproduced.

FIG. 6 is cross-sectional views showing two types of optical discs thatcan be loaded into an optical disc drive according to a first preferredembodiment of the present invention.

FIG. 7 is a block diagram showing an optical disc drive according to thefirst preferred embodiment of the present invention.

FIG. 8 illustrates an exemplary configuration for a spherical aberrationproducer, which can be used effectively in an optical disc driveaccording to the present invention.

FIG. 9 shows how to detect a spherical aberration.

FIG. 10 shows waveforms of spherical aberration error signals.

Portion (a) of FIG. 11 shows how an output signal of an aberration errordetector changes with the magnitude of spherical aberration, and portion(b) of FIG. 11 shows how an output signal of a validity verifier changeswith the magnitude of spherical aberration.

FIG. 12 is a block diagram showing an optical disc drive according to asecond preferred embodiment of the present invention.

FIG. 13 is cross-sectional views showing optical discs, which may beused in an optical disc drive according to the second or fifth preferredembodiment of the present invention.

FIG. 14 is a block diagram showing an optical disc drive according to athird preferred embodiment of the present invention.

FIG. 15 is a block diagram showing an optical disc drive according to afourth preferred embodiment of the present invention.

FIG. 16 is a plan view illustrating an optical disc, which may be usedin the fourth preferred embodiment.

FIG. 17 shows the waveform of an FE signal obtained from a double-layeroptical disc.

FIG. 18 is a block diagram showing an optical disc drive according to afifth preferred embodiment of the present invention.

Portion (a) of FIG. 19 shows an output signal of an FE generatoraccording to the fifth preferred embodiment, portion (b) of FIG. 19shows an output signal of a focusing instructor according to the fifthpreferred embodiment, and portion (c) of FIG. 19 shows the sources ofdrive signals to be selected by a control switch.

FIG. 20 is a block diagram showing an optical disc drive according to asixth preferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

Hereinafter, an optical disc drive according to a first preferredembodiment of the present invention will be described with reference tothe accompanying drawings.

An optical disc drive according to this preferred embodiment can readand write data from/on at least two types of optical discs such as thoseshown in FIG. 6. One of the two types of optical discs shown in FIG. 6has one information layer, while the other has two information layers. Alaser beam for reading and writing data is radiated toward the substratefrom under the disc shown in FIG. 6.

In the example illustrated in FIG. 6, the depth of the information layerof the single-layer optical disc, that of the lower information layer(which will be referred to herein as a “first information layer”) of thedouble-layer optical disc, and that of the upper information layer(which will be referred to herein as a “second information layer”) ofthe double-layer optical disc are all different from each other.Accordingly, if the depth of an information layer, on which the focalpoint of the light beam is located, can be detected, then it is possibleto determine, by the detected depth of the information layer, whetherthe optical disc being irradiated with the light beam is a single-layeroptical disc or a double-layer optical disc. Also, if the optical discbeing irradiated with the light beam is already known as a double-layeroptical disc, it is also possible to determine on which of the twoinformation layers of the double-layer optical disc the focal point ofthe light beam is currently located.

In this preferred embodiment, the depth of each information layer isassociated with the magnitude of correction to be made on the sphericalaberration of a light beam (i.e., a variation to be caused in an opticalsystem in order to minimize the spherical aberration), and the depth ofany information layer is sensed by obtaining the magnitude of sphericalaberration correction to make.

An optical system for minimizing the magnitude of spherical aberrationchanges its state with the depth of the information layer. On the otherhand, the state of an optical system that has been regulated so as tominimize the spherical aberration can be evaluated by voltage, currentand other parameters to drive the optical system. That is to say, themagnitude of spherical aberration correction to make can be estimatedfrom these parameters. Accordingly, the values of these parameters(i.e., the magnitudes of spherical aberration corrections) can beassociated with the depths of information layers.

According to the present invention, a mechanism for changing thespherical aberration is provided for an optical disc drive and driven inaccordance with an electrical signal (i.e., a drive signal), therebyminimizing the spherical aberration. And the magnitude of sphericalaberration correction to make is detected based on the value (e.g., thevoltage level) of the drive signal when the spherical aberration isminimized. By comparing the detected value of the drive signal (i.e.,the magnitude of spherical aberration correction) with a prestored valuein the memory of the optical disc drive, the depth of the informationlayer can be sensed.

Hereinafter, a configuration for an optical disc drive according to thispreferred embodiment will be described with reference to FIG. 7. In FIG.7, any component, having the same function as the counterpart shown inFIG. 1, is identified by the same reference numeral as that used in FIG.1.

As shown in FIG. 7, the optical disc drive of this preferred embodimentis an apparatus that can read and/or write data from/on a loaded opticaldisc 1 and includes a mechanism for rotating the optical disc 1 with amotor (not shown), an optical head 10 for irradiating the rotatingoptical disc 1 with laser light, and a section for driving the opticalhead 10 and processing and controlling the output signals of the opticalhead.

The optical head 10 includes a laser light source 11, a condenser lens13, a polarization beam splitter 12, an Fc actuator 14, a Tk actuator15, a photodetector 16 and a spherical aberration producer 17.

The spherical aberration producer 17 of the optical head 10 changes thespherical aberration at the focal point of a light beam. First, aconfiguration for the spherical aberration producer 17 will be describedwith reference to FIG. 8.

The spherical aberration producer 17 of this preferred embodimentincludes a convex lens and a concave lens as a set. As shown in FIG. 8,by changing the distance between the convex and concave lenses, thelight beam emitted from the laser light source turns from one ofdiverging light, parallel light and converged light into another. If thelight beam entering the condenser lens 13 is diverging light, then theaberration between the focal point of the light that has beentransmitted through the center portion of the condenser lens 13 and thatof the light that has been transmitted through the peripheral portion ofthe condenser lens 13, i.e., the spherical aberration, is relativelylarge. On the other hand, if the light beam entering the condenser lens13 is converged light, then the aberration with respect to the focalpoint of the light transmitted through the peripheral portion of thecondenser lens 13, i.e., the spherical aberration, is relatively small.

In this manner, by changing the distance between the convex and concavelenses of the spherical aberration producer 17, the spherical aberrationcan be adjusted. The distance between the convex and concave lenses ofthe spherical aberration producer 17 is controllable by regulating themagnitude of voltage or current applied to the actuator or motor thatdrives the convex lens.

The spherical aberration producer 17 does not have to have the exemplaryconfiguration shown in FIG. 8. For example, the spherical aberration mayalso be controlled by changing the state of the light beam that is goingto enter the condenser lens 13 with a liquid crystal layer of which therefractive index changes with a voltage applied thereto.

In this preferred embodiment, the amplitude of the voltage (i.e., drivesignal) applied to the spherical aberration producer 17 corresponds tothe magnitude of resultant spherical aberration. That is to say, themagnitude of spherical aberration can be estimated by the amplitude ofthe voltage (drive signal) applied to the spherical aberration producer17. As described above, in a situation where the light beam has beenconverged onto a particular information layer, if the amplitude of thevoltage (or drive signal) applied to the spherical aberration producer17 is regulated so as to minimize the spherical aberration, then themagnitude of that drive signal corresponds to the depth of theinformation layer.

Look at FIG. 7 again.

The optical disc drive of this preferred embodiment further includes anaberration error detector 60 for detecting the spherical aberration anda validity verifier 61 and an aberration regulator 62 for changing thespherical aberration according to the detected magnitude of thespherical aberration.

In accordance with the signal supplied from the photodetector 16, theaberration error detector 60 generates a signal representing themagnitude of spherical aberration at the focal point of the light beam(which will be referred to herein as a “spherical aberration signal”).This spherical aberration signal is send to the validity verifier 61 andaberration regulator 62.

The spherical aberration signal, generated by the aberration errordetector 60 of this preferred embodiment, shows a sine waveform if thespherical aberration is equal to or smaller than a predetermined valuebut becomes approximately equal to zero if the spherical aberrationincreases and exceeds the predetermined value. If the sphericalaberration signal supplied from the aberration error detector 60 has anon-zero absolute value, then the validity verifier 61 outputs ahigh-level signal, meaning “valid”, to the aberration regulator 62. Onthe other hand, if the spherical aberration signal has an absolute valueof approximately zero, then the validity verifier 61 outputs a low-levelsignal to the aberration regulator 62. That is to say, in performing theoperation of reducing the spherical aberration, first, the sphericalaberration producer 17 is driven such that the output signal of thevalidity verifier 61 changes from the low level into the high level.Once the output of the validity verifier 61 has gone high, the sphericalaberration producer 17 is driven such that the sine wave portion of thespherical aberration signal becomes equal to zero. Hereinafter, thispoint will be described in further detail.

The aberration regulator 62 sequentially performs the followingtwo-stage regulating operations, thereby outputting a drive signal tothe spherical aberration producer 17 and disc type recognizer 63.

First, in the first stage of the regulating operation, the aberrationregulator 62 drives the spherical aberration producer 17 such that theoutput signal of the validity verifier 61 goes high. For example, bygradually changing the voltage level of the drive signal for thespherical aberration producer 17 (which will be referred to herein as a“spherical aberration correction signal”), the aberration regulator 62changes the spherical aberration within a wide range. Then, theaberration regulator 62 senses the value of the spherical aberrationcorrection signal when the output signal of the validity detector 61changes from the low level into the high level. In the second stage ofthe regulating operation, the aberration regulator 62 makes a fineadjustment on the voltage level of the spherical aberration correctionsignal to drive the spherical aberration producer 17, thereby correctingthe aberration such that the output signal of the aberration errordetector 60 crosses zero with respect to the reference level.

In accordance with the drive signal supplied from the aberrationregulator 62, the disc type recognizer 63 detects the distance from thesurface of the optical disc 1, on which the light beam is incident, tothe information layer, on which the focal point of the light beam islocated (i.e., the depth of the information layer), thereby recognizingthe type of the optical disc based on the depth of the informationlayer.

Next, it will be described in detail with reference to FIG. 9 how todetect the spherical aberration in this preferred embodiment. In FIG. 9,the hatched portions represent cross sections of the light beam.

In this preferred embodiment, the light beam that has been reflectedfrom the optical disc is split into an inside beam portion and anoutside beam portion through a hologram, for example. Then, the insideportion of the light beam is allowed to be incident on a photodiode 16a, while the outside portion thereof on a photodiode 16 b. In theexample illustrated in FIG. 9, each of the photodiodes 16 a and 16 bincludes four separate light detecting portions and generates anelectrical signal representing the intensity of the light that theselight detecting portions have received.

The aberration error detector 60 shown in FIG. 7 receives the respectiveoutputs of the photodetector 16, including those of the photodiodes 16 aand 16 b, and generates an inside FE signal and an outside FE signal forthe inside and outside portions of the light beam, respectively, by thesame method as that used to generate the FE signal.

As shown in FIG. 5, the spherical aberration is an aberration producedbetween the focal point of a light beam passing the inside portion ofthe condenser lens 13 and that of a light beam passing the outsideportion of the condenser lens 13. Accordingly, the magnitude of thespherical aberration produced can be detected by calculating thedifference between the inside and outside FE signals. In this preferredembodiment, the difference between the inside and outside FE signals isused as a signal representing the magnitude of spherical aberrationproduced (i.e., the spherical aberration signal), and the sphericalaberration producer 17 of the optical head 10 is driven underpredetermined conditions so as to reduce the value of this sphericalaberration signal. In other words, the spherical aberration signal ismade to cross zero by controlling the level of the signal supplied tothe spherical aberration producer 17 to drive it (i.e., the sphericalaberration correction signal).

Next, it will be described in detail with reference to FIG. 10 how tocorrect the spherical aberration. FIG. 10 shows cross sections of twotypes of optical discs and the waveforms of spherical aberration signalsin a situation where the focal point of the light beam is located righton the information layer of each optical disc.

As can be seen from FIG. 10, when the light beam is focused on theinformation layer, the magnitude of the spherical aberration correctionsignal at the zero-crossing point of the spherical aberration signalchanges with the depth of the information layer. As shown on theleft-hand side of FIG. 10, if the information layer is relativelyshallow, the spherical aberration signal crosses zero when the sphericalaberration correction signal has a comparatively small value.Conversely, if the information layer is relatively deep, the sphericalaberration signal crosses zero when the spherical aberration correctionsignal has a comparatively large value as shown on the right-hand sideof FIG. 10.

As also shown in FIG. 10, the spherical aberration signal is a signal tobe generated based on the FE signal detection principle, and therefore,has as limited an error detection range as the FE signal. Accordingly,the spherical aberration signal becomes zero outside of the limitederror detection range. More specifically, the aberration correctionsignal shown in FIG. 10 includes a portion with a substantially sinewaveform (i.e., a valid portion) and portions with zero amplitude.

Next, it will be described in detail with reference to FIG. 11 how thevalidity verifier 61 operates.

As described above, the spherical aberration signal, generated by theaberration error detector 60, has its detection range. Portion (a) ofFIG. 11 shows the output spherical aberration signal of the aberrationerror detector 60, while portion (b) of FIG. 11 shows the output signalof the validity verifier 61. In portions (a) and (b) of FIG. 11, theabscissa represents the magnitude of the spherical aberration correctionsignal to drive the spherical aberration producer 17.

If the spherical aberration signal, output from the aberration errordetector 60, remains zero for a predetermined amount of time, thevalidity verifier 61 generates a low-level signal. Accordingly, as shownin portion (b) of FIG. 11, the output signal of the validity verifier 61is high within the detection range of the spherical aberration signal.

In the first stage of its regulating operation, the aberration regulator62 changes the level of the spherical aberration correction signal,thereby searching for a level of the spherical aberration correctionsignal at which the output of the validity verifier 61 goes high. Whenthe output of the validity verifier 61 reaches the high level, theaberration regulator 62 enters the second stage of its regulatingoperation. Specifically, the aberration regulator 62 regulates the levelof the spherical aberration correction signal such that the sphericalaberration signal, supplied from the aberration error detector 60,crosses zero with respect to the reference level. More particularly, theaberration regulator 62 drives the spherical aberration producer 17 suchthat the spherical aberration signal crosses zero with respect to thereference level, and stores, in a memory, the level of the sphericalaberration correction signal when the spherical aberration signalcrosses zero with respect to the reference level.

In this manner, the spherical aberration is minimized in accordance withthe distance from the information layer on which the focal point of thelight beam is located to the surface of the substrate (i.e., the depthof the information layer), and the value of the spherical aberrationcorrection signal that minimizes the spherical aberration is detected.This value changes with the depth of the information layer. Thus, thedepth of a target information layer can be determined by the value ofthe spherical aberration correction signal that minimizes the sphericalaberration.

The disc type recognizer 63 senses the depth of the information layer bythe value of the spherical aberration correction signal that minimizesthe spherical aberration. More specifically, the disc type recognizer 63includes means for comparing the value of the spherical aberrationcorrection signal that minimizes the spherical aberration with apredetermined value stored in a memory (not shown), and determines,based on the result of comparison, what information layer the value ofthe spherical aberration correction signal that minimizes the sphericalaberration is associated with. As shown in FIG. 5, the information layerof the single-layer optical disc and the lower and upper informationlayers of the double-layer optical disc have mutually different depths.Accordingly, based on that value of the spherical aberration correctionsignal corresponding to the depth of the information layer, the disctype recognizer 63 can locate the information layer on which the lightbeam is converged and focused. The disc type recognizer 63 can alsodetermine, according to that value of the spherical aberrationcorrection signal corresponding to the depth of the information layer,whether the optical disc being irradiated with the light beam is asingle-layer optical disc or a double-layer optical disc.

In the preferred embodiment described above, the aberration regulator 62regulates the spherical aberration by using the spherical aberrationsignal supplied from the aberration error detector 60 and the outputsignal of the validity verifier 61. However, if the spherical aberrationsignal, supplied from the aberration error detector 60, has asufficiently wide detection range, then the aberration regulator 62 mayregulate the spherical aberration using only the spherical aberrationsignal supplied from the aberration error detector 60.

Conversely, if the spherical aberration signal has a sufficiently narrowdetection range, then the aberration regulator 62 may regulate thespherical aberration using only the output signal of the validityverifier 61.

Optionally, the aberration regulator 62 may also regulate the amplitudeof the spherical aberration correction signal supplied to the sphericalaberration producer 17 in accordance with a TE signal, representing howmuch the focal point of the light beam deviates from the track, suchthat the amplitude of the TE signal is maximized. In that case, a valueof the spherical aberration correction signal that maximizes theamplitude of the TE signal corresponds to the “depth of informationlayer”.

In the preferred embodiment described above, single-layer anddouble-layer optical discs are recognized. However, an optical disc withthree or more information layers may also be distinguished from othertypes of optical discs. In any case, to recognize the type of a givenoptical disc by the depth of the information layer in a short time, thedepth of an information layer closest to the surface (i.e., thelowermost layer) of one optical disc to be recognized is preferablydifferent from that of the lowermost layer of another.

It should be noted that the voltage to drive the focus actuator alsochanges with the depth of the information layer. However, the focusactuator is driven such that the focal point of the light beam can stillcatch up with the information layer even if the focal point shiftswithin a broad range of 300 μm to 400 μm due to the flutter of theoptical disc. For that reason, an information layer depth of about 100μm cannot be estimated accurately according to the level of the signalto drive the focus actuator. On the other hand, the spherical aberrationcan be corrected at a resolution of 30 μm or less in the depthdirection. Thus, according to this preferred embodiment, the depth ofthe information layer can be sensed with high precision.

Embodiment 2

Hereinafter, an optical disc drive according to a second preferredembodiment of the present invention will be described with reference toFIG. 12. In FIG. 12, any component having the same function as thecounterpart shown in FIG. 7 or 1 is identified by the same referencenumeral as that used in FIG. 7 or 1 and the description thereof will beomitted herein.

The optical disc drive of this preferred embodiment includes an FEgenerator 30 and a TE generator 40 just like the conventional opticaldisc drive shown in FIG. 1 and also includes an aberration errordetector 60, a validity verifier 61 and an aberration regulator 62 justlike the preferred embodiment shown in FIG. 7. Unlike the optical discdrive shown in FIG. 7, the optical disc drive of this preferredembodiment further includes an address detector 64 and a disc typerecognizer 65.

In the optical disc drive of this preferred embodiment, the outputsignal of the photodetector 16 is transmitted to not only the FEgenerator 30, TE generator 40 and aberration error detector 60 but alsoto the address detector 64. The address detector 64 detects the addresson the optical disc 1, at which the focal point of the light beam islocated, and then notifies the disc type recognizer 65 of the detectionresult.

On the other hand, the aberration regulator 62 operates just as alreadydescribed for the first preferred embodiment and outputs a value of theaberration correction signal that minimizes the spherical aberration tothe disc type recognizer 65.

If the address information provided by the address detector 64 isgreater than a predetermined value or if the level of the signalsupplied from the aberration regulator 62 (i.e., the value of theaberration correction signal that minimizes the spherical aberration) isout of a prescribed range, the disc type recognizer 65 of this preferredembodiment recognizes the optical disc 1 loaded in the optical discdrive as a double-layer optical disc.

On the other hand, if the address information provided by the addressdetector 64 is smaller than the predetermined value or if the level ofthe signal supplied from the aberration regulator 62 (i.e., the value ofthe aberration correction signal that minimizes the sphericalaberration) is within the prescribed range, then the disc typerecognizer 65 recognizes the optical disc 1 loaded in the optical discdrive as a single-layer optical disc.

The optical disc drive of this preferred embodiment can recognize thetwo types of optical discs such as those shown in FIG. 13 while beingstarted up. FIG. 13 schematically illustrates cross sections of asingle-layer optical disc and a double-layer optical disc. As shown inFIG. 13, each optical disc is irradiated with a light beam that has comefrom under the optical disc.

In the optical discs shown in FIG. 13, the information layer of thesingle-layer optical disc and the upper information layer of thedouble-layer optical disc have the same depth. Also, in the double-layeroptical disc, addresses, representing locations on the tracks, aresequentially allocated to the shallower information layer closer to thesurface of the optical disc and then to the deeper layer. Accordingly,the minimum address value is present on the shallower information layerthat is closer to the surface of the optical disc on which the lightbeam is incident, while the maximum address value is present on thedeeper information layer that is more distant from the surface of theoptical disc on which the light beam is incident. Consequently, it ispossible to determine, by the address value detected, on whichinformation layer of the double-layer optical disc the focal point ofthe light beam is currently located.

As in the first preferred embodiment described above, the aberrationregulator 62 of this preferred embodiment also drives the sphericalaberration producer 17 so as to minimize the spherical aberration at thefocal point of the light beam. As also described above, the value of thespherical aberration correction signal that minimizes the sphericalaberration has a level corresponding to the depth of the informationlayer of the optical disc 1 on which the focal point of the light beamis currently located.

In the optical disc drive of this preferred embodiment, when thetracking control gets ON after the optical disc drive has been startedup, the address detector 64 reads out an address that was recorded on atrack of the optical disc 1.

If the information layer on which the focal point of the light beam islocated is the first information layer as counted from the lightincident surface of the double-layer optical disc, then the depth ofthat information layer is different from that of the information layerof the single-layer optical disc. Thus, the type of that optical discand the level of the information layer of the optical disc can bedetected.

On the other hand, if the information layer on which the focal point ofthe light beam is located is the second information layer as countedfrom the light incident surface of the double-layer optical disc and ifthe depth of that information layer is the same as that of theinformation layer of the single-layer optical disc, then the type of thegiven optical disc cannot be recognized directly by the drive valuesupplied from the aberration regulator 62. However, the address valueallocated to that information layer of the double-layer optical disc isdifferent from that allocated to the information layer of thesingle-layer optical disc. Thus, the type of the given optical disc canalso be recognized by the address value provided by the address detector64.

According to this preferred embodiment, the optical disc 1 beingirradiated with the light beam is recognized as either the single-layeroptical disc or the double-layer optical disc in this manner.

As in the first preferred embodiment described above, the aberrationregulator 62 of this preferred embodiment also regulates the sphericalaberration by using the spherical aberration signal supplied from theaberration error detector 60 and the output signal of the validityverifier 61. However, if the spherical aberration signal has asufficiently wide detection range, then the aberration regulator 62 mayregulate the spherical aberration using only the spherical aberrationsignal. Conversely, if the spherical aberration signal has asufficiently narrow detection range, then the aberration regulator 62may regulate the spherical aberration using only the output signal ofthe validity verifier 61. Furthermore, the aberration regulator 62 mayalso regulate the amplitude of the spherical aberration correctionsignal such that the amplitude of a TE signal, representing how much thefocal point of the light beam deviates from the track, is maximized.Then, the depth of the information layer may be sensed according to thevalue of the spherical aberration correction signal that maximizes theamplitude of the TE signal.

Embodiment 3

Hereinafter, an optical disc drive according to a third preferredembodiment of the present invention will be described with reference toFIG. 14. In FIG. 14, any component having the same function as thecounterpart shown in FIG. 2 is identified by the same reference numeralas that used in FIG. 2 and the description thereof will be omittedherein.

The optical disc drive of this preferred embodiment includes a bestlight intensity table 68, an allowable light intensity table 70, a bestlight intensity selector 69, an initial light intensity selector 71, aselection index generator 72, and a light intensity selector 73.

The disc type recognizer 67 of this preferred embodiment recognizes thetype of a given optical disc in accordance with a signal supplied from areflected light quantity detector 66 and outputs a signal, representingthe result of recognition, to the best light intensity selector 69. Thedisc type recognizer 67 may have a configuration for recognizing thetype of a given optical disc according to the same principle as thatalready described for the first and second preferred embodiments. Thedisc type recognizer 67 sends a low-level signal to the light intensityselector 73 while still recognizing the type of the optical disc, butsends a high-level signal to the light intensity selector 73 afterhaving recognized the type of the optical disc.

The best light intensity table 68 stores information about the bestlight intensities for multiple types of optical discs, from/on whichthis optical disc drive can read and/or write data.

The best light intensity selector 69 selects one of the best lightintensities from the best light intensity table 68 in accordance withthe recognition result of the disc type recognizer 67 and then outputs asignal, representing the light intensity selected, tot the lightintensity selector 73.

The allowable light intensity table 70 stores information about highestpossible light intensities, at or under which the information stored onthe multiple types of optical discs to be processed by the optical discdrive of this preferred embodiment is never lost.

The selection index generator 72 supplies an index signal to the initiallight intensity selector 71 so as to instruct the initial lightintensity selector 71 to select the weakest light intensity. Inaccordance with the index signal supplied from the selection indexgenerator 72, the initial light intensity selector 71 selects theweakest light intensity from the allowable light intensity table 70 andsupplies a signal, representing the light intensity selected, to thelight intensity selector 73.

If the signal supplied from the disc type recognizer 67 is low, thelight intensity selector 73 selects the light intensity, provided by theinitial light intensity selector 71, for the laser light source 11. Onthe other hand, if the signal supplied from the disc type recognizer 67is high, the light intensity selector 73 selects the light intensity,provided by the best light intensity selector 69, for the laser lightsource 11. In response, the laser light source 11 radiates a light beamhaving the specified intensity toward the optical disc 1.

In this preferred embodiment, the following three types of optical discscan be processed, for example. A first optical disc may have a readlight intensity of 0.3 mW and an allowable light intensity (at or underwhich the information stored on the information layer does not alter) of0.5 mW. A second optical disc may have a read light intensity of 0.6 mWand an allowable light intensity (at or under which the informationstored on the information layer does not alter) of 1.0 mW. A thirdoptical disc may have a read light intensity of 0.9 mW and an allowablelight intensity (at or under which the information stored on theinformation layer does not alter) of 1.5 mW.

In this case, the three values of 0.3 mW, 0.6 mW and 0.9 mW are storedon the best light intensity table 68, while the three values of 0.5 mW,1.0 mW and 1.5 mW are stored on the allowable light intensity table 70.While the disc type recognizer 67 has not recognized the type of thegiven optical disc yet, the value of 0.5 mW is selected by the initiallight intensity selector 71 and specified by the light intensityselector 73 for the laser light source 11. Once the disc type recognizer67 has recognized the type of the optical disc, a value associated withthe disc type recognized is selected by the best light intensityselector and then specified by the light intensity selector 73 for thelaser light source 11.

According to this preferred embodiment, the start up process can beperformed without altering any information on the information layerbefore the type of the given optical disc is recognized, no matter whattype of disc has been loaded.

In the preferred embodiment described above, the weakest light intensityis supposed to be selected from the allowable light intensity table asthe light intensity before the type of the given optical disc has beenrecognized. Alternatively, the weakest value may be selected from thebest light intensity table. As another alternative, the best lightintensity of a type of optical disc with the smallest number ofinformation layers may be selected from the best light intensity table.

Embodiment 4

Hereinafter, an optical disc drive according to a fourth preferredembodiment of the present invention will be described with reference toFIG. 15. In FIG. 15, any component having the same function as thecounterpart shown in FIG. 14 is identified by the same reference numeralas that used in FIG. 14 and the description thereof will be omittedherein.

The transport motor 76 shown in FIG. 15 is driven by a transport targetgenerator 74 and a transport drive generator 75 functioning as transportdriving means.

A signal representing the result of disc type recognition is transmittedfrom a disc type recognizer 67 to the transport target generator 74. Inaccordance with the recognition result, the transport target generator74 supplies a signal, representing a target position to which theoptical head 10 should be transported, to the transport drive generator75.

The transport drive generator 75 generates a signal, which drives thetransport motor 76 such that the transport motor 76 transports theoptical head 10 to exactly the same position as the transport targetposition, and supplies that signal to the transport motor 76. Inresponse to the drive signal supplied from the transport drive generator75, the transport motor 76 transports the optical head 10 in thetracking direction.

FIG. 16 illustrates an optical disc to be read from and written to bythe optical disc drive of this preferred embodiment. The optical discshown in FIG. 16 has two zones, of which the boundary is defined so asto intersect with the radial direction. The outer zone is an area, whichdata can not only be written on by changing the intensity of the lightbeam but also be read from by sensing the quantity of the light beamreflected. On the other hand, the inner zone is an area, on whichmanagement information such as the number of information layers isstored as track wobbles and from which only the management informationcan be read. In multiple types of optical discs, the boundary betweenthe rewritable zone and the read-only zone is defined at the same radiallocation.

The optical disc drive of this preferred embodiment could also processan optical disc on which the boundary is defined at a different radiallocation. However, the quantity of light reflected from such an opticaldisc is significantly different from that of light reflected from theoptical disc described above. Accordingly, the disc type recognizer 67can determine, according to the signal supplied from the reflected lightquantity detector 66, whether or not the given optical disc is the typeshown in FIG. 16.

When the disc type recognizer 67 recognizes the optical disc 1 loaded inthe optical disc drive as the type shown in FIG. 16, the transporttarget generator 74 transmits a signal, setting the central radiallocation of the inner zone of the optical disc shown in FIG. 16 as thetarget location, to the transport drive generator 75. While checking theposition of the transport motor 76, the transport drive generator 75drives the transport motor 76 such that the focal point of the lightbeam is shifted to the central radial location of the inner zone.Thereafter, focus control and tracking control are started, and thenumber of information layers of the given optical disc 1 is sensed basedon the information represented by the wobbles (i.e., managementinformation). Then, the best light beam intensity is selected accordingto the number of information layers, thereby starting the optical discdrive up.

Since the inner zone of the optical disc shown in FIG. 16 is a read-onlyarea, the information stored there as wobbles is never alterableirrespective of the intensity of the light beam. Accordingly, no matterwhat type of optical disc has been given, the start up process can becarried out without altering the information stored on the informationlayer of the given optical disc before recognizing its type.

As described above, according to this preferred embodiment, the numberof information layers of the optical disc 1 is sensed based on themanagement information stored as track wobbles on the optical disc.

It should be noted that if an FE signal is obtained by shifting thefocal point of the light beam in the focus direction without rotatingthe optical disc 1 at all and if the given optical disc is adouble-layer optical disc, for example, then a signal having thewaveform shown in FIG. 17 can be obtained. By counting the number ofsuch curves appearing near the information layers (which will bereferred to herein as “S-curves”), the number of information layers ofthe optical disc 1 can also be obtained. In that case, the S-curve alsoappears on the outermost surface of the optical disc. Thus, the numberof information layers is actually obtained by subtracting one from thenumber of S-curves counted. If only the S-curve on the surface of theoptical disc appeared during such counting, the accuracy of measurementcould be increased by counting the number again.

Embodiment 5

Hereinafter, an optical disc drive according to a fifth preferredembodiment of the present invention will be described with reference toFIG. 18. In FIG. 18, any component having the same function as thecounterpart shown in FIG. 3 is identified by the same reference numeralas that used in FIG. 3 and the description thereof will be omittedherein.

The optical disc drive of this preferred embodiment includes anapproaching drive generator 80, a departing drive generator 81 and adirection selector 82, which together functions as search driving means.

In the optical disc drive of this preferred embodiment, the outputsignal of the photodetector 16 is supplied not only to the FE generator30 but also to the reflected light quantity detector 66. In response tothe signal supplied from the photodetector 16, the reflected lightquantity detector 66 transmits a signal, representing the quantity oflight reflected from the optical disc 1, to the disc type recognizer 67.In accordance with the signal supplied from the reflected light quantitydetector 66, the disc type recognizer 67 determines whether or not theoptical disc loaded in the optical disc drive has the configurationshown in FIG. 13. If the answer is YES, then the disc type recognizer 67sends a high-level signal to the direction selector 82. Otherwise, thedisc type recognizer 67 sends a low-level signal to the directionselector 82. Alternatively, the disc type recognizer 67 may also have aconfiguration for recognizing the type of the optical disc on the sameprinciple as that already described for the first and second preferredembodiments.

The approaching drive generator 80 transmits a drive signal, instructingthat the condenser lens 13, located away from the optical disc 1, bebrought toward the optical disc 1, to the direction selector 82. On theother hand, the departing drive generator 81 transmits a drive signal,instructing that the condenser lens 13 be brought away from the opticaldisc 1, to the direction selector 82.

If the high-level signal is supplied from the disc type recognizer 67,then the direction selector 82 passes the output signal of the departingdrive generator 81 to a control switch 78. On the other hand, if thelow-level signal is supplied from the disc type recognizer 67, then thedirection selector 82 passes the output signal of the approaching drivegenerator 80 to the control switch 78.

FIG. 13 illustrates cross sections of two types of optical discs to beprocessed by the optical disc drive of this preferred embodiment. Asshown in FIG. 13, each optical disc is irradiated with a light beam thathas come from under the optical disc.

As shown in FIG. 13, the information layer of the single-layer opticaldisc and the second information layer of the double-layer optical dischave the same depth. The optical disc drive of this preferred embodimentcould also process other types of optical discs with differentinformation layer depths from those of the two types of optical discsshown in FIG. 13. However, the quantity of light reflected from any ofthose optical discs is significantly different from that of lightreflected from the optical disc described above. Accordingly, the disctype recognizer 67 can determine, according to the signal supplied fromthe reflected light quantity detector 66, whether or not the givenoptical disc is the type shown in FIG. 13.

Next, it will be described with reference to portions (a) through (c) ofFIG. 19 how the optical disc drive of this preferred embodiment performsa focusing operation. Portion (a) of FIG. 19 shows the output FE signalof the FE generator 30 shown in FIG. 18, portion (b) of FIG. 19 showsthe output signal of a focusing instructor 77, and portion (c) of FIG.19 shows the sources of drive signals to be selected by the controlswitch 78.

In portions (a) through (c) of FIG. 19, the abscissa represents thetime. On recognizing the given optical disc 1 as one of the two types ofoptical discs shown in FIG. 13, the disc type recognizer 67 of thispreferred embodiment sends a high-level signal to the direction selector82. In response, the direction selector 82 passes the output signal ofthe departing drive generator 81 to the control switch 78. In theinitial stage of the startup operation, the control switch 78 selectsthe drive signal supplied from the direction selector 82, therebyshifting the focal point of the light beam, which has been converged bythe condenser lens 13, away from the optical disc 1.

When the FE signal supplied from the FE generator 30 crosses zero afterhaving decreased from its reference level FELVL, the output signal ofthe focusing instructor 77 changes from the low level into the highlevel. As of that moment, the control switch 78 selects the outputsignal of the Fc filter 31, thus turning the focus control ON. In thiscase, the focus control is carried out on the information layer, whichis most distant from the surface of the optical disc. Specifically, inthe single-layer optical disc, the only information layer is subjectedto the focus control. On the other hand, in the double-layer opticaldisc, the information layer that is the second deepest as counted fromthe light incident plane of the optical disc is subjected to the focuscontrol. These two information layers have the same depth as shown inFIG. 13 and there is no need to adjust the spherical aberration.

In the apparatus of recognizing the type of the given optical disc 1based on the optical disc information stored on the optical disc 1, thetime it takes to complete the recognition does not increase by the timeit takes to adjust the spherical aberration, and therefore, the startuptime does not increase, either.

In the preferred embodiment described above, the deepest informationlayer, which is most distant from the surface, is as deep as theinformation layer of the single-layer optical disc. Thus, the focusingoperation is carried out with the focal point of the light beam shiftedaway from a close position. However, if the shallowest informationlayer, which is closest to the surface, is as deep as the informationlayer of the single-layer optical disc, then the focusing operation maybe carried out with the focal point of the light beam shifted from adistant position toward the optical disc.

Embodiment 6

Hereinafter, an optical disc drive according to a sixth preferredembodiment of the present invention will be described with reference toFIG. 20. In FIG. 20, any component having the same function as thecounterpart shown in FIG. 18 or 3 is identified by the same referencenumeral as that used in FIG. 18 or 3 and the description thereof will beomitted herein.

The optical disc drive of this preferred embodiment includes a table 91on which information about the depths of information layers is stored, aselector 92 and an aberration correction generator 93.

The table 91 stores the depths of all information layers of multipletypes of optical discs to be read from and written to by this opticaldisc drive.

The selector 92 receives a signal representing the recognition resultfrom the disc type recognizer 67. Also, the selector 92 retrieves theinformation layer depths of all optical discs that can be loaded intothis optical disc drive from the table 91 and calculates the averagethereof. This average is passed to the aberration correction generator93. In accordance with the signal supplied from the selector 92, theaberration correction generator 93 generates a spherical aberrationcorrection signal, thereby driving the spherical aberration producer 17.

In response to the spherical aberration correction signal supplied fromthe aberration correction generator 93, the spherical aberrationproducer 17 changes the spherical aberration at the focal point of thelight beam. After the spherical aberration has been corrected, thefocusing operation is performed as already described for the prior art.

Suppose the single-layer optical disc shown in FIG. 6 has an informationlayer depth of 109 μm and the double-layer optical disc has informationlayer depths of 80 μm and 120 μm, respectively. If the disc typerecognizer 67 recognizes the optical disc, loaded in the optical discdrive, as either the single-layer optical disc or the double-layeroptical disc shown in FIG. 6, then the selector 92 sends a signal,representing the average depth of 109 μm of these three informationlayers, to the aberration correction generator 93. According to thispreferred embodiment, the average of possible information layer depthsis known before the focusing operation is started. Thus, thedeterioration of the FE signal can be minimized. Consequently, thefocusing operation can be stabilized.

In the preferred embodiment described above, the average of all possibleinformation layer depths is calculated and used. Alternatively, only themaximum and minimum values can be extracted from those possibleinformation layer depths and then their average may be calculated andused.

In the preferred embodiments described above, the single-layer anddouble-layer optical discs are supposed to be loaded. However, theoptical disc drive of this preferred embodiment may also be loaded withan optical disc with three or more information layers.

INDUSTRIAL APPLICABILITY

An optical disc drive according to the present invention detects thedepth of an information layer of the given optical disc, on which thelight beam is currently converged, in accordance with the state of anoptical system that is needed to minimize the spherical aberration.Then, based on the detected depth of the information layer, the opticaldisc drive can recognize the type of the optical disc that has beenloaded thereto. According to the present invention, an optical discdrive to be loaded with a rewritable multilayer optical disc can bestarted up quickly.

A next-generation optical disc, having higher storage capacity than aDVD, uses a light beam having a shorter wavelength and a condenser lenshaving a higher NA as compared with a DVD. For that reason, the opticaldisc drive thereof needs to be provided with a mechanism for correctingthe spherical aberration. According to the present invention, thedistance between the information layer and the surface of the disc issensed, and the type of the given optical disc is recognized, by usingsuch a mechanism. Thus, the type of the given optical disc can berecognized quickly without increasing the cost significantly.

1. An optical disc drive for reading and/or writing data from/on anoptical disc, having at least one information layer, by using a lightbeam, the optical disc drive comprising: a spherical aberrationdetecting section for generating a spherical aberration signalrepresenting a spherical aberration that has been produced at a focalpoint of the light beam on the information layer of the optical disc; aspherical aberration changing section for changing the sphericalaberration; a spherical aberration regulating section for generating anaberration correction signal to correct the spherical aberration bydriving the spherical aberration changing section; a memory for storinginformation on relationship between predetermined values of theaberration correction signal and distances from information layers ofdifferent types of optical discs to the surface of the optical discs;and means for detecting a value of the aberration correction signal thatminimizes the spherical aberration in a situation where the focal pointof the light beam is located on the information layer of the opticaldisc and for detecting the depth of the information layer, whichcorresponds to a distance from the information layer on which the focalpoint of the light beam is located to the surface of the optical disc,by comparing the value detected with the predetermined values of theaberration correction signal stored on the memory.
 2. The optical discdrive of claim 1, further comprising comparing means for comparing thevalue of the aberration correction signal, which minimizes the sphericalaberration in the situation where the focal point of the light beam islocated on the information layer of the optical disc, with apredetermined value.
 3. The optical disc drive of claim 2, wherein ifthe optical disc, irradiated with the light beam, has a plurality ofinformation layers, the optical disc drive determines, based on acomparison result obtained by the comparing means, on which of theinformation layers the focal point of the light beam is currentlylocated.
 4. The optical disc drive of claim 2, wherein the optical discdrive recognizes, based on a comparison result obtained by the comparingmeans, the type of the optical disc being irradiated with the lightbeam.
 5. The optical disc drive of claim 2, wherein the optical discdrive detects, based on a comparison result obtained by the comparingmeans, the number of the information layers that the optical disc beingirradiated with the light beam has.
 6. The optical disc drive of claim2, wherein if the optical disc, irradiated with the light beam, has aplurality of information layers, the optical disc drive determines,based on a comparison result obtained by the comparing means and addressinformation acquired from the information layer on which the focal pointof the light beam is located, on which of the information layers thefocal point of the light beam is currently located.
 7. The optical discdrive of claim 1, wherein the optical disc drive detects a quantity,corresponding to a distance from the surface of the optical disc to oneof the information layers that is closest to the surface of the opticaldisc, thereby recognizing the optical disc being irradiated with thelight beam based on the quantity detected.
 8. The optical disc drive ofclaim 1, further comprising: converged beam irradiating means forconverging the light beam and irradiating the optical disc with theconverged light beam; a focus regulating section for shifting the focalpoint of the light beam, which has been converged by the converged beamirradiating means, perpendicularly to the information layers of theoptical disc; a focus error signal detecting section for generating asignal representing the deviation of the focal point of the light beamfrom each said information layer of the optical disc; and a focuscontrol driving section for driving the focus regulating section inresponse to a signal supplied from the focus error signal detectingsection such that the focal point of the light beam catches up with theinformation layer of the optical disc.
 9. The optical disc drive ofclaim 1, further comprising: a tracking error detecting section fordetecting a signal representing a positional relationship between thefocal point of the light beam and a track on the optical disc; and anamplitude detecting section for detecting the amplitude of a signalsupplied from the tracking error detecting section, wherein thespherical aberration regulating section drives the spherical aberrationchanging section so as to maximize a signal supplied from the amplitudedetecting section.
 10. The optical disc drive of claim 1, wherein thespherical aberration regulating section drives the spherical aberrationchanging section so as to make the signal supplied from the sphericalaberration detecting section equal to zero.
 11. The optical disc driveof claim 10, further comprising a judging section for judging thevalidity of the spherical aberration signal supplied from the sphericalaberration detecting section, wherein the spherical aberrationregulating section drives the spherical aberration changing section suchthat the judging section recognizes the validity of the sphericalaberration signal and then drives the spherical aberration changingsection such that the spherical aberration signal supplied from thespherical aberration detecting section becomes zero.
 12. The opticaldisc drive of claim 1, further comprising judging means for judging thevalidity of the spherical aberration signal supplied from the sphericalaberration detecting section, wherein the spherical aberrationregulating section drives the spherical aberration changing section suchthat the judging means recognizes the validity of the sphericalaberration signal.